In recent years, with higher functionality of IC cards and greater storage capacity of memory cards, an electronic circuit device has been demanded that mounts semiconductor elements and other components with high density. Still, with higher functionality and reduction in the size and weight of mobile devices, an electronic circuit device requires higher functionality and compactification. For a memory card, for example, how to increase its storage capacity within its standardized size is important. For a circuit substrate, meanwhile, as well as an approach to increase packaging density by miniaturization of connection pitches and multilayering, technology has been positively developed to increase packaging density by stacking module substrates mounting semiconductor elements and electronic components therein, in a multilayered manner.
Japanese Patent Unexamined Publication No. 2002-207986 (described as “patent document” hereinafter) discloses a memory card with the following structure as shown in FIG. 16. That is, memory module substrates 420 mounting memory chip 410 on one side of mother substrate 400 are stacked in a two-layered manner; circuit control element 430 for controlling the above-described memory chip 410 is mounted on the other surface of mother substrate 400; and they are incorporated into housing 480.
In this memory card, memory module substrates 420 are connected to each other with Cu ball 440 or an elastic body covered with a conductive film, with a diameter of approximately 300 μm. In the same way, the bottom surface of memory module substrate 420 at the lower side is connected to mother substrate 400 with Cu ball 450 or an elastic body covered with a conductive film. Further, the top surface of mother substrate 400 is loaded thereon with chip capacitor 460 for bypassing, and the bottom surface is provided thereon with connecting terminal 470.
In a conventional electronic circuit device described in the patent document, the memory module substrates are connected to each other with a Cu ball or an elastic body covered with a conductive film, and so are the memory module substrate and the mother substrate. However, the Cu ball needs to secure a certain distance between the substrates to prevent memories from contacting each other, by means of its size, and thus the size cannot be reduced.
Wiring connection can be performed only in one direction: from the memory module substrate to the mother substrate. Further, a memory module substrate on which different ICs such as logic ICs and ASICs are combined has more electrodes as the number of stacked layers increases, thus requiring minute wiring connections. Consequently, miniaturization is difficult in wiring connection with Cu balls, but is possible if Cu balls are arranged in a staggered manner so as not to contact each other. In this case, however, the area for connection electrodes increases, and thus the packaging area for semiconductor elements and others undesirably decreases.
In the above-described connection process, a Cu ball or elastic body is difficult to be fixed at a given position, thus resulting in poor workability and yields.
In addition, requiring a mother substrate causes the space for mounting semiconductor elements to be limited, thus making miniaturization and slimming down difficult. For a device with a standardized size particularly, such as a memory card, the packaging space is strictly limited. That is to say, an attempt to increase the number of semiconductor elements to expand the memory capacity is unsuccessful due to the constant standardized size of the memory card. An IC card has a similar standard mainly for its thickness.
Eventually, how to mount in a housing of a standardised size remains to be solved in these electronic circuit devices.
These electronic circuit devices, which are mass-produced items, require favorable workability and a method for manufacturing with easy automatization, along with high reliability.
Meanwhile, when a memory card is deformed, the module substrate itself bends with a Cu ball as the supporting point, and thus the mounted semiconductor elements and the like are undesirably prone to break.